PSA stands for Prostate Specific Antigen. It is used to screen for the presence of prostate cancer. Normally most of the PSA remains in the prostate gland and very little is released into the blood stream. When there are diseased or cancerous cells present in the prostate gland more PSA leaks out into the blood stream. While the normal range for PSA is any value below 4.0 ng/ml, another factor to consider is PSA velocity. Over time, PSA values should stay about the same or may slightly creep up. Therefore, when a PSA value increases significantly from one year to the next even if it is still below 4.0 ng/dl, it calls for further evaluation. What is considered significant? This is still up for debate in scientific circles, but some research points to a year to year increase of 0.75 ng/dl as being quite significant.